--2. Define a tree type that has only one constructor, like our Java example. Instead of
--the Empty constructor, use the Maybe type to refer to a node’s children.

data Tree a = Node a (Maybe (Tree a)) (Maybe (Tree a))
              deriving (Show)

simpleTree = Node "parent" (Just (Node "left child" Nothing Nothing))
                           (Just (Node "right child" Nothing Nothing))
